In order to achieve a smaller, thinner semiconductor package, a package having a structure in which only one side (semiconductor die side) of a lead frame is molded and exposed leads on the reverse side are used for external connection has been developed in recent years. A package with this structure has the advantages of achieving a smaller, thinner semiconductor package since the leads do not project from a molding resin. For example, a method in which, after an adhesive tape is laminated to one side of a lead frame, a chip is mounted on the opposite side of the lead frame, wire bonded, and molded, and subsequently the adhesive tape is peeled off has been proposed (ref. e.g. Japanese Patent Application Laid-open No. 10-12773 (Claim 4), Japanese Patent Application Laid-open No. 2000-294580 (Claim 1)). However, when a lead frame is used, there are restrictions on the thickness and the material of the lead frame, and there are the problems that the semiconductor package is still high, fine wiring cannot be formed, etc.
As another method for producing a semiconductor package that is similar to the above-mentioned package, a method has been proposed in which, after a metal layer is formed on a temporary support substrate, a circuit is formed, and a chip is mounted, wire bonded, and molded, the temporary support substrate is peeled off, but it is not clear what properties are required for the temporary support substrate in order to prevent resin from going around between the wiring circuit and the support substrate when molding, and to prevent glue residue from being present on the wiring circuit after peeling off the support substrate (ref. e.g. Japanese Patent Application Laid-open No. 11-121646 (Claims 4 and 5, [0013][0018])).